Continuous crossover between insulating ferroelectrics and the polar metals: \textit{Ab initio} calculation of structural phase transitions of Li$B$O$_3$ ($B$ = Ta, W, Re, Os)

TL;DR

This study uses ab initio calculations to explore structural phase transitions in LiBO3 compounds, predicting a new polar metal and revealing a continuous crossover from insulating ferroelectrics to polar metals driven by electron doping.

Contribution

It predicts LiWO3 as a polar metal and demonstrates the continuous crossover between ferroelectric insulators and polar metals through electron doping, supported by detailed phonon calculations.

Findings

LiReO3, LiTaO3, and LiOsO3 undergo polar-nonpolar phase transitions at specific temperatures.

LiWO3 is predicted to be a polar metal yet to be experimentally confirmed.

Electron doping suppresses transition temperature, enabling crossover from insulator to metal.

Abstract

Inspired by the recent discovery of a new polar metal LiReO$_3$ by K. Murayama, \textit{et al}, we calculate the temperature($T$)-dependent crystal structures of Li$B$O3 with $B$ = Ta, W, Re, Os, using the self-consistent phonon (SCPH) theory. We have reproduced the experimentally observed polar-nonpolar structural phase transitions and the transition temperatures ($T_c$) of LiTaO$_3$, LiReO$_3$, and LiOsO$_3$. From the calculation, we predict that LiWO$_3$ is a polar metal, which is yet to be tested experimentally. Upon doping electrons to the insulating LiTaO$_3$, the predicted $T_c$ is quickly suppressed and approaches those of the polar metals. Thus, there is a continuous crossover between ferroelectric insulators and polar metals if we dope electrons to the polar metals. Investigating the detailed material dependence of the interatomic force constants (IFCs), we explicitly show that the suppression of $T_c$ in polar metals can be ascribed to the screening of the long-range Li-O interaction, which is caused by the presence of the itinerant electrons.